Esters of vinylphosphonic acid serve as useful synthons, i.e. precursors, for the preparation of agriculturally active compounds. Uses range from plant growth regulators to phosphatase inhibitors to pesticides. The versatility of this intermediate material resides in the reactivity of the vinylic group towards nucleophiles. The application of this reactivity via reaction with alcohols, thiols, amines, nitroalkanes or active methylene compounds results in this wide class of agricultural chemicals.
Vinylphosphonates also undergo Diels-Alder reactions with dienes. Polymerizaton or co-polymerization has resulted in the preparation of heat and light stabilizers for polymers as well as flame retardant or shrinkage retardant additives.
Heretofore, synthetic approaches to the formation of vinylic phosphonates have centered on direct replacement of the vinylic halide with trivalent phosphorous esters. With the exception of .alpha.,.beta.-unsaturated systems, reactions involving simple Michaelis-Arbuzov reaction conditions have failed. Similarly, reactions involving transition metal salts as catalysts have found greater utility but are still limited to the reaction of aromatic or vinylic halides with phosphites or similar trivalent phosphorus compounds as disclosed, for example, in U.S. Pat. No. 3,493,639. Because of apparent severe reaction conditions involved in these syntheses, industrial aplication of these reaction products have been limited.
It is thus apparent that a need exists for an improved practical and efficient method for the preparation of vinyl phosphonate diesters.